Persons with hearing impairment are often fitted with hearing aids. In such cases the degree of hearing loss often is greater in one ear than the other. Usually the audiologist considers that the most important remedy is to provide a hearing aid on the assumption that this will solve the problem of the hearing impaired person, and not a great deal of regard is taken of the psychological aspects of hearing remedy. A hearing aid for one ear is usually prescribed.
In the use of a hearing aid for one ear, usually the volume is turned up by the user to a comfortable hearing level. Even if there is some level of hearing in the other ear, it has been found that the ability to locate the source of sound is lost. Furthermore, background noises interfere substantially with the understanding of speech where there is a significant background noise level, such as at a party. Often the person wearing the hearing aid finds it difficult to distinguish between the words spoken by a person directly to him, and the words spoken by a loud talker some distance away or behind him.
Particularly for people who have lost hearing in both ears and who wish to locate the source of sounds, sometimes two hearing aids are prescribed, one for each ear. It has been found that while this can increase the intelligibility of voices or other sounds being heard, it does not readily solve the problem of poor sound location, except in some exceptional circumstances, such as when a talker is directly in front of the hearing impaired listener.
While the problem of peripheral sounds masking the sound that the hearing impaired listener wishes to hear remains, and can even be compounded when two hearing aids are used, the lack of ability to locate the source of the sound is caused by what is known as the shadow effect. In the case in which the talker is to the side of the listener who has a pair of hearing aids, the head forms an acoustic shadow over the hearing aid microphone which is farthest from the talker. This results in an incorrect, significantly lower level of sound in the ear which is furthest from the talker, making the person wearing the hearing aid think that the source of sound is further to the side than it actually is. The shadow effect is very significant and for most unexpected sounds makes quick location of the source of the sounds virtually impossible. This can be embarrassing under some circumstances, and dangerous in others, for example where the dual hearing aid wearer crosses the street and attracts a warning horn from an uncoming vehicle to one side of the wearer.
In addition, while there have been continual advances in miniaturization of hearing aids, most hearing aids are still noticeable to others. In old fashioned hearing aids the wearer had a belt pack for carrying a microphone, amplifier and batteries, and a wire led inside the wearer's clothing, up the neck, to an earphone. More recent hearing aids have been built into the temples of eyeglasses (as in U.S. Pat. No. 3,665,121 issued May 23, 1971 to Beltone Electronics Corporation), or are fitted around the top of the ear with the microphone, amplifier and transducer in a case behind the ear and an acoustic tube leading to an earplug over the ear and into the ear, etc. To some wearers, the observeable presence of the hearing aid is embarrassing.